JPH0985446A - Gas shielded arc welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas shielded arc welding method without causing any hot crack (pear shape crack) even in the case of performing back-bead welding in butt welding at a higher current and a faster speed than for the first pass welding conditions. SOLUTION: By using two or more electrodes 21, 22, a distance L between a first electrode 21 and a second electrode 22 in the welding direction is controlled to <=100mm, and simultaneously the polarities of the first electrode 21 and the second electrodes 22 are made invert to each other. Thus a sound welding is performed under a stable arc condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas shielded arc welding method, and more particularly, to a single-sided carbon dioxide gas arc welding method and a MAG welding method in a butt joint.

[0002]

2. Description of the Related Art The most important point regarding welding conditions is to keep the initial layer welding conditions according to the type, diameter, and welding position of the wire. When welding at a higher current and faster speed than the initial layer welding conditions, the risk of first layer (backside) bead cracking increases accordingly. Further, as shown in FIG. 2, the crack resistance of the first layer beads of the flux-cored wire is generally inferior to that of the solid wire. Therefore, in the case of the flux-cored wire, it is necessary to manage the welding condition sufficiently.

For example, using a flux-cored wire,
When the backside welding of the butt welding is performed with a large welding current of 50 Amp or more, high temperature cracks (pear-shaped cracks) occur in the temporary attachment parts.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object the following:
It is an object of the present invention to provide a gas shielded arc welding method in which hot cracking (pear-shaped cracking) does not occur even when performing backside welding of butt welding at a higher current and faster speed than the initial layer welding conditions.

[0005]

That is, the gas shielded arc welding method of the present invention uses two or more electrodes and the distance L between the first electrode and the second electrode in the welding direction.
Is 100 mm or less, and the polarities of the first electrode and the second electrode are reversed. At that time, in order to stabilize the arc, a filler (a powdery or granular iron material) may be filled in the groove.

[0006] By welding with the first electrode in the welding direction, impurities (S, P, etc.) in the molten metal segregate at the center of the welded portion, causing high temperature cracking. Hot cracking can be prevented by energizing the arc of the electrode. For this purpose, it is necessary to bring the first electrode and the second electrode close to each other.
When the 1st electrode is brought close to each other, the arcs magnetically interfere with each other and the arc becomes unstable and welding becomes impossible. Therefore, the polarities of the 1st electrode and the 2nd electrode are reversed to stabilize the arc, Enables sound welding.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, a carbon dioxide automatic arc welding apparatus 10 used for carrying out the method of the present invention has three carbon dioxide automatic arc welding parts 11, 12, 13 arranged in a row in the welding direction A. Is equipped with.

The distance L between the electrode 21 of the first arc welded portion 11 and the electrode 22 of the second arc welded portion 12 is set to 80 ± 20 mm, while the electrode 21 of the first arc welded portion is set. Is set to be positive, and the polarity of the electrode 22 at the second arc weld is set to be negative. In addition,
On the contrary, it goes without saying that the polarity of the electrode 21 of the first arc welded portion may be negative and the polarity of the electrode 22 of the second arc welded portion may be positive.

The first and second arc welds 11 and 1
2 is a predetermined angle θ ₁ (+ 5 °) toward the welding direction A
Tilted forward and the third arc weld 13 is in the welding direction A
In contrast, it is warped backward by a predetermined angle θ ₂ (−5 °). In addition, in FIG. 1, 31 is a steel plate and 32 is a backing material. While advancing the carbon dioxide automatic arc welding device 10 in the welding direction indicated by the symbol A, the three carbon dioxide automatic arc welding parts 11, 12, 1 are advanced.
3 and start the butt welding of the steel plate 31,
Before the welding initial layer welded by the electrode 21 of the first arc welding portion causes hot cracking, the arc of the electrode 22 of the second arc welding portion is energized to prevent hot cracking.
In addition, since the polarities of the electrode 21 of the first arc welded portion and the electrode 22 of the second arc welded portion are opposite to each other, there is no magnetic interference with each other, and sound welding can be performed under a stable arc. Done. At that time, in order to stabilize the arc, a filler (a powdery or granular iron material) may be filled in the groove.

[0010]

【Example】

(Example 1) When a joint which had been plate-welded by conventional one-sided carbon dioxide semi-automatic welding was welded using the multi-electrode large-current one-sided carbon dioxide automatic welding method of the present invention, the welding time was shortened and the welding work was performed. Mitigation has become possible. That is, the welding time can be shortened to about 1/7 when the plate thickness is 16 mm,
In the case of 0 mm, it could be shortened by about 1/10.

A) Conventional method: -Semi-automatic one-side carbon dioxide welding (assuming working current 260A, arc time rate 50%)-Welding time: About 36 minutes / m for a plate thickness of 16 mm, about 54 for a plate thickness of 20 mm Min / m b) The method of the present invention: ・ One-sided carbon dioxide automatic welding (assuming a working current of 400 A and an arc time of 100%) ・ Welding time: When the plate thickness is 16 mm, about 5 min / m (two electrodes are used) In the case of 20 mm, about 5 minutes / m (3 electrodes used) ・ Electrode spacing: 80 ± 20 mm

[0012]

As described above, the present invention uses two or more electrodes and sets the distance L between the first electrode and the second electrode in the welding direction to 100 mm or less and Since the polarities of the second electrode and the second electrode are reversed, the occurrence of high temperature cracks (pear-shaped cracks) can be prevented even if backside welding of butt welding is performed at a higher current and faster speed than the first layer welding conditions. It became possible to do.

[Brief description of drawings]

FIG. 1 is a schematic view of a carbon dioxide automatic welding apparatus used for carrying out the method of the present invention.

FIG. 2 is a diagram showing crack resistance of single-sided welding.

[Explanation of symbols]

 21, 22, 23 Electrode A Welding direction L Distance between the 1st electrode and the 2nd electrode

Claims (2)

[Claims] 1. An electrode having two or more electrodes, wherein a distance L between the first electrode and the second electrode in the welding direction is 100.
A gas shielded arc welding method, characterized in that the first electrode and the second electrode have opposite polarities while being less than or equal to mm. 2. The gas shielded arc welding method according to claim 1, wherein the filler is filled in the groove.